Silver articles turn black when kept in the open for longer time due to the formation of _________.

Silver articles turn black when exposed to air due to a process called corrosion or tarnishing [2]. This occurs because silver (Ag) reacts with sulfur-containing compounds in the atmosphere, primarily hydrogen sulfide (H2S). The chemical reaction between silver and hydrogen sulfide, often in the presence of oxygen, results in the formation of a thin, dark layer of silver sulfide on the metal's surface [1]. The chemical formula for this black compound is Ag2S. While silver is generally unreactive with oxygen even at high temperatures, it has a high affinity for sulfur, making Ag2S the most stable oxidized compound under normal atmospheric conditions [3]. This black coating can be removed through chemical reduction using aluminum or by using abrasive polishes.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.5 CORROSION > p. 53
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > 1.3.1 Corrosion > p. 13
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > Activity 3.9 > p. 42